1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device constituted of semiconductor elements typified by thin film transistors (hereinafter referred to as TFTs) using a crystalline semiconductor film formed on a substrate. Semiconductor devices manufactured in accordance with the present invention include not only elements such as a TFT and a MOS transistor but also a liquid crystal display device having a semiconductor circuit constituted of the above insulating gate type transistors (a microprocessor, a signal processing circuit, a high frequency circuit or the like), an EL (electro luminescence) display device, an EC (electro chromic) display device, an image sensor, and the like.
2. Description of the Related Art
At present, TFTs are used in integrated circuits as semiconductor elements using a semiconductor film, and particularly, as switching elements of an image display device. Further, TFTs in which a crystalline semiconductor film with higher mobility than that of an amorphous semiconductor film used in active layers have high driving ability, and are used also as elements of a driver circuit.
In the present situation, an amorphous silicon film or a crystalline silicon film (also referred to as a polysilicon film) is mainly used as active layers.
As a method of obtaining a crystalline silicon film, a method of performing a heating process, a laser annealing method, and a technique disclosed in Japanese Patent Application Laid-open Nos. Hei 6-232059 and Hei 7-130652 by applicants of the present invention are known. The technique disclosed in these applications is such that a crystalline silicon film with excellent crystallinity can be formed by conducting a heating process at 500 to 600° C. for about 4 hours utilizing a metal element (particularly, nickel) that promotes crystallization of silicon.
Furthermore, in recent years, low-priced glass has been used for a substrate in order to manufacture a display device with a large screen at a low price. In order to prevent contamination due to an alkali metal element such as sodium (Na) contained in this glass substrate, a base film formed of an inorganic insulating film such as a silicon oxide film, a silicon nitride film or a silicon oxide nitride film is provided between an amorphous silicon film and the glass substrate.
In general, in a case where the above base film is formed, oxygen gas or nitrogen gas is used as material gas, and on the other hand, in a case where the amorphous silicon film is formed, only silane (SiH4) gas is used as material gas. Accordingly, in order to obtain a satisfactory amorphous silicon film, a film forming chamber for a base film and a film forming chamber for an amorphous silicon film needs to be formed in lamination. Thus, a plurality of film formation chambers or film forming devices are provided, and film formation is performed in the respective dedicated chambers. Therefore, because a substrate is conveyed, there have been problems such as the increase in process time and the reduction in yield due to conveyance trouble.
Further, even if continuous formation (formation of lamination by continuously forming films without exposure to an atmosphere) from the formation of the base film through the formation of the amorphous silicon film can be performed in a single chamber, since the amorphous silicon film formed in the single chamber contains a large amount of impurities such as oxygen, nitrogen and fluorine which are factors of obstructing crystallization, it has been difficult to obtain a satisfactory crystalline silicon film by using a known crystallization technique.